Why Is My House Turning Green?
You clean your house, and for a while it looks great.
Then one day you notice a little green area on the siding.
A few months later, there is more of it.
You may also notice that one side of your house gets dirty much faster than the others.
Why does this happen?
Usually, the answer comes down to a few things:
Moisture + shade + organic growth + time.
Understanding what is growing or collecting on your home is important because different problems need different cleaning methods.
What Is the Green Stuff on My Siding?
The green buildup you see on siding is often some type of organic growth, commonly algae or similar biological buildup.
It tends to grow where conditions stay damp.
That is why you may see more green growth:
On shaded sides of the house
Behind bushes and trees
Under rooflines
Around gutters and downspouts
Near areas that stay damp
On parts of the house that receive less direct sunlight
The growth doesn't necessarily mean there is something wrong with your house.
Outdoor surfaces are constantly exposed to moisture, pollen, dirt, spores, insects, leaves, and the environment.
Over time, buildup happens.
Why Is One Side of My House Greener?
This is extremely common.
Walk around your house and compare all four sides.
You may find that one wall looks almost perfectly clean while another is covered in green growth.
One major reason is sunlight.
A side of the house that gets plenty of direct sun usually dries faster.
A shaded side may stay damp much longer.
Trees can make the problem even worse by blocking sunlight and keeping the area cooler and wetter.
So if you're wondering:
“Why does this side keep getting dirty?”
Look around.
Are there trees?
Is it shaded?
Does water collect nearby?
Does that side take longer to dry after rain?
Those clues can tell you a lot.
Eastern North Carolina Makes a Difference
Here in Eastern North Carolina, we deal with warm temperatures, humidity, rain, trees, pollen, and long periods of moisture.
Those conditions can be great for organic growth.
Homes around New Bern and the surrounding communities may develop green buildup on siding, fences, concrete, roofs, and other exterior surfaces simply because of the environment.
That doesn't mean every house needs to be washed on exactly the same schedule.
A heavily shaded home surrounded by trees may need attention sooner than a home sitting in an open area with lots of sunlight.
That's why at Pro Wash Pressure Washing, we believe homeowners should pay attention to the condition of the home, not just the calendar.
What About the Black Stuff?
Not every dark area is the same thing.
Black or dark discoloration can come from several different sources.
It may be:
Organic growth
Dirt
Mildew or mold-like growth
Roof-related biological growth
Gutter staining
Pollution or environmental buildup
A stain that requires a different cleaning process
This is where exterior cleaning becomes more complicated.
You should identify the problem before choosing the solution.
If you assume every black mark is ordinary dirt, you may use the wrong cleaner or too much pressure trying to remove something that pressure alone won't fix.
What About Pollen?
If you live in North Carolina, you already know about pollen.
During pollen season, outdoor surfaces can become covered in yellow or greenish dust.
You'll see it on:
Cars • Porches • Siding • Windows • Outdoor furniture • Decks • Railings
Pollen is different from established organic growth.
It can collect on top of the surface and mix with dirt, moisture, and other contaminants.
This is another reason your home can look dirty even when there isn't heavy algae growth.
Why Are My Gutters Black?
This one is important.
If you see dark lines or streaks running down the outside of white gutters, don't automatically assume they are ordinary mold.
Some gutter staining can be more strongly bonded to the surface and may require a separate cleaning process beyond a normal house wash.
Oxidation can also change how a painted or coated surface looks.
This is why a professional shouldn't simply keep increasing pressure when a stain doesn't disappear.
Sometimes:
The problem isn't that you need more pressure. You need to correctly identify the stain.
We'll talk much more about gutters later in this guide.
What Is Oxidation?
Oxidation is another problem homeowners sometimes mistake for dirt.
Over time, sun and weather can affect exterior surfaces and coatings.
On some siding or painted surfaces, you may notice a faded or chalky appearance.
If you rub your hand across the surface, you may even see a chalk-like residue on your fingers.
That can be oxidation.
And this distinction matters because oxidation is not the same thing as algae.
A normal house wash designed to remove organic growth may not restore an oxidized surface to its original appearance.
Oxidation may require a separate restoration process.
Why Identifying the Stain Comes First
Imagine going to a doctor and saying:
“Something hurts.”
Before deciding what to do, they would need to know where it hurts and what is causing it.
Exterior cleaning is similar.
Before attacking a stain, ask:
What am I looking at?
Is it green organic growth?
Is it pollen?
Is it ordinary dirt?
Is it rust?
Is it oxidation?
Is it oil?
Is it gutter staining?
Is it damage to the actual surface?
Different problems require different solutions.
Why Doesn't Water Alone Always Work?
Suppose your siding is covered in green organic growth.
You could point a pressure washer at it and try to physically blast everything away.
It may look cleaner.
But you're relying on water pressure to do the work.
With professional house washing, the idea is different.
An appropriate cleaning solution is applied to the surface and given time to work on the organic growth.
At Pro Wash, the house-washing process includes a dwell period rather than immediately rinsing the solution away. The treated area is then inspected, and another application can be made if growth remains.
This is another example of the Perfectly Clean™ principle:
Don't fight the dirt harder. Understand what you're cleaning.
Can I Keep My House From Ever Turning Green?
Probably not forever.
Your home lives outside.
Rain will fall.
Pollen will blow.
Trees will drop debris.
Humidity will rise.
Shade will keep certain areas damp.
Organic material will eventually return.
But you can pay attention to the conditions around your property.
For example, keeping landscaping maintained, addressing drainage problems, cleaning gutters when needed, and keeping excessive vegetation away from exterior surfaces may help reduce some moisture-related conditions.
Regular exterior cleaning can then become maintenance instead of waiting until the buildup becomes severe.
The Perfectly Clean™ Inspection
Here's something you can do today.
Walk outside and slowly circle your house.
Don't just look at the siding.
Start at the top.
Look at your:
Roof → Gutters → Soffits → Fascia → Windows → Trim → Siding → Foundation → Concrete → Decks and fences
Look for:
Green growth
Black streaks
Dirt
Pollen
Rust-colored stains
Chalky or faded surfaces
Heavy buildup
Areas that stay wet
Areas hidden by plants
Differences between sunny and shaded sides
You're not cleaning anything yet.
You're learning to see the property first.
That is exactly where a good cleaning process should begin.
Perfectly Clean™ Quick Lesson
GREEN BUILDUP
Often → Organic growth
YELLOW DUST
Often → Pollen
CHALKY OR FADED SIDING
May be → Oxidation
DARK GUTTER STREAKS
May require → Specialty cleaning
RUST-COLORED STAIN
May require → Specialty stain treatment
SHADED, DAMP AREAS
Often → Growth returns faster
And remember:
Identify first. Clean second.